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From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Daniel Henrique Barboza <danielhb413@gmail.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	qemu-ppc@nongnu.org, Cedric Le Goater <clg@kaod.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Ingo Molnar <mingo@kernel.org>,
	David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [PATCH 1/3] powerpc/smp: Reintroduce cpu_core_mask
Date: Thu, 15 Apr 2021 23:06:24 +0530	[thread overview]
Message-ID: <20210415173624.GD2633526@linux.vnet.ibm.com> (raw)
In-Reply-To: <20210415171134.GA16351@in.ibm.com>

* Gautham R Shenoy <ego@linux.vnet.ibm.com> [2021-04-15 22:41:34]:

> Hi Srikar,
> 
> 

Thanks for taking a look.

> > @@ -1485,12 +1486,36 @@ static void add_cpu_to_masks(int cpu)
> >  	add_cpu_to_smallcore_masks(cpu);
> > 
> >  	/* In CPU-hotplug path, hence use GFP_ATOMIC */
> > -	alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu));
> > +	ret = alloc_cpumask_var_node(&mask, GFP_ATOMIC, cpu_to_node(cpu));
> >  	update_mask_by_l2(cpu, &mask);
> > 
> >  	if (has_coregroup_support())
> >  		update_coregroup_mask(cpu, &mask);
> > 
> > +	if (chip_id == -1 || !ret) {
> > +		cpumask_copy(per_cpu(cpu_core_map, cpu), cpu_cpu_mask(cpu));
> > +		goto out;
> > +	}
> > +
> > +	if (shared_caches)
> > +		submask_fn = cpu_l2_cache_mask;
> > +
> > +	/* Update core_mask with all the CPUs that are part of submask */
> > +	or_cpumasks_related(cpu, cpu, submask_fn, cpu_core_mask);
> >
> 
> If coregroups exist, we can add the cpus of the coregroup to the
> cpu_core_mask thereby reducing the scope of the for_each_cpu() search
> below. This will still cut down the time on Baremetal systems
> supporting coregroups.
> 

Yes, once we upstream coregroup support to Baremetal, we should look
at adding it. Also do note, number of CPUs we support for Baremetal is
comparatively lower than in PowerVM + QEMU. And more importantly the
number of cores per coregroup is also very low. So the optimization
may not yield too much of a benefit.

Its only in the QEMU case, where we end up having too many cores in
the same chip, where we see a drastic increase in the boot-up time.

-- 
Thanks and Regards
Srikar Dronamraju

  reply	other threads:[~2021-04-15 17:37 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-15 12:09 [PATCH 0/3] Reintroduce cpu_core_mask Srikar Dronamraju
2021-04-15 12:09 ` [PATCH 1/3] powerpc/smp: " Srikar Dronamraju
2021-04-15 17:11   ` Gautham R Shenoy
2021-04-15 17:36     ` Srikar Dronamraju [this message]
2021-04-16  3:21   ` David Gibson
2021-04-16  5:45     ` Srikar Dronamraju
2021-04-19  1:17       ` David Gibson
2021-04-15 12:09 ` [PATCH 2/3] Revert "powerpc/topology: Update topology_core_cpumask" Srikar Dronamraju
2021-04-15 12:09 ` [PATCH 3/3] powerpc/smp: Cache CPU to chip lookup Srikar Dronamraju
2021-04-15 17:19   ` Gautham R Shenoy
2021-04-15 17:51     ` Srikar Dronamraju
2021-04-16 15:57       ` Gautham R Shenoy
2021-04-16 16:57         ` Srikar Dronamraju
2021-04-19  1:19         ` David Gibson
2021-04-15 12:17 ` [PATCH 0/3] Reintroduce cpu_core_mask Daniel Henrique Barboza
2021-04-19  4:00 ` Michael Ellerman

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